1. Field of the Invention
The present invention relates to a surface mount coil using a drum core.
2. Description of the Related Art
A conventional surface mount coil using a drum core has been extensively used and is constructed such that, as shown in FIG. 1, a round insulated wire is wound around a spool portion 53 of a drum core 50 which is integrated with a top flange 51 and a base flange 52 so as to constitute a drum core 50 and both ends of the round insulated wire is connected to respective connecting terminals of plate-like metallic lead frames 55 and 55. The plate-like metallic lead frames 55 and 55 are adhesively fixed to the drum core thereby constituting a pair of terminal electrodes of the coil. The electrodes have been conventionally called “lead frame type electrodes”. In addition, although not shown, there are other types structured such that lead terminals are provided on an insulating board made of resin and adapted for receiving a coil and winding ends are connected to the lead terminals, thereby constituting electrodes, such that electrode materials are coated at a portion on a drum core and baked and winding ends are connected to the coated portion thereby constituting electrodes, or such that winding ends are bound around and soldered to a flange of a drum core thereby constituting electrodes.
Furthermore, there is another type surface mount coil using a drum core, which is structured such that a rectangular insulated wire is wound edgewise. Since this type of coil is superior to the type using the round insulated wire in winding efficiency ratio of wire space to winding space, it is advantageous in reduction in size and profile and also in that the wire is flat and can be used as plate-like metallic electrodes.
The above mentioned types of surface mount coils with round insulated wires wound therearound have had the following defects.
In the type where the both ends of the round insulated wire are bound around and connected to the connecting terminals of the plate-like metallic lead frames, its production cost is increased because the lead frames (the electrodes) have to be discretely provided, and an additional operation process is required for fitting the lead frames thus involving a cost increase.
In the type where the lead terminals are provided on the insulating board made of resin, and winding ends are connected to the coated portion thereby constituting electrodes, a cost increase is involved due to additional materials, specifically the electrode materials, and also due to an additional operation process for coating and baking the electrode materials.
The type, where winding ends are bound around and soldered to the flange of the drum core thereby constituting electrodes, has a limited allowable value of current and therefore cannot be used in a heavy-current circuit, and also often incurs shakiness when mounted on a printed circuit board.
Furthermore, although another type coil, where the rectangular insulated wire is wound edgewise, is superior to the coil using the round insulated wire in reduction in profile, number of parts, manufacturing operation, and allowable value of current, it has the following reliability problems. Specifically, this type coil suffers a decreased soldered area of the winding ends constituting electrodes due to the soldered portion peeling off from the core or plastic board and flatness shakes and is lifted off when mounted on a printed circuit board.